The present invention concerns a metal seal plug and, particularly, a metal seal plug for use in sealing off a tubing run in an underwater oil and/or gas well system. It is an improvement on the metal seal tubing plug described in U.S. Pat. No. 4,178,992 which issued Dec. 18, 1979 to Louis M. Regan et al. Both plugs utilize a metal-to-metal seal which provides a reliable wire-line or tubing installable and retrievable plug for subsea tubings. A metal-to-metal type seal has superior seal reliability over conventional resilient elastomer-type seals. Materials chosen for the metal seals are less susceptible to failure and resultant leaks than available elastomer materials. Elastomer seal systems are susceptible to deterioration due to age, gas infusion, cold flow or creep.